1. Field of the Invention
The invention relates to a device for fixing rivets, buttons, etc., which comprises an article lower part and an article upper part, to a fabric or the like, with a lower gripper supporting the article lower part and a plunger, which performs the riveting stroke and with whose lower end is associated an upper gripper acting on the article upper part and with whose upper end is associated a drive mechanism ensuring the stroke movement, and with a finger guard bow, associated with the plunger and extending into the movement path of the upper gripper and which, following the release of a plunger riveting stroke, on encountering an obstacle stops the drive mechanism and therefor the plunger before reaching its end position.
2. Description of the Related Art
Fixing machines for clothing and leather accessories, as well as fasteners, which are formed by riveting machines, are subject to safety regulations, governing the shaft use by the final consumer. Virtually all the safety measures taken are disadvantageous from the handling standpoint, for the rapid removal of faults and for inspection of the working area. Therefore particular importance is attached to the safety devices. These lead to not inconsiderable costs compared with the overall machine costs. Apart form the electrical safety regulations which apply, it is necessary to respect regulations for the danger zone in the working area of the machine, where the upper gripper is moved towards the lower gripper. In this area the most serious injuries to hands and fingers can occur if adequate safety measures are not taken. According to existing guidelines access to this area must be secured in such a way that the safety spacing, i.e. the remaining opening width during the working stroke movement is equal to or smaller than 4 mm.
Manufacturers have developed different systems in order to satisfy this requirements. As the working area for loading and unloading must be as large as possible, it is necessary to secure and/or control the danger zone between the upper and lower grippers prior to the working stroke. For this purpose it is known to bind the upper gripper to the plunger in such a way that it opens a contact as soon as an obstacle occurs in the danger zone. The drive is immediately subject to braking by means of the brake of the brake motor drive and the working stroke is interrupted. As a massive gripper is used for scanning the danger zone, painful contacts with the fingers and fingernails in the danger zone give rise to blue spots, although the permitted power of 50 N for the safety system is not exceeded.
A pneumatic system is also known, in which the drive is switched in pressure less manner as soon as the plunger strikes an obstacle during its downward movement.
Finally a device of the aforementioned type is known with the aid of which hand and finger injuries can be effectively avoided in that besides the main drive mechanism for the plunger drive there is an additional drive mechanism for driving the leading finger guard bow. Only when the latter has traversed the danger zone within a predetermined time up to the lower and point, is the main drive mechanism started and the plunger performs the working stroke. Admittedly this system operates safely, but requires considerable control expenditure and an additional drive mechanism. Moreover, disadvantageously, the machining period is slowed down by the lead time of the finger guard bow.